The Neuropsychology study involved 41 adults with diabetes and 424 adults in good health, between ages 53 and 90.

The research confirmed previous reports that diabetes impairs cognition and added two important findings. First, it teased out the specific domains hurt by diabetes.

Second, it revealed that the performance gap was not worse in the older group. Thus, the reductions in executive function and processing speed seem to begin earlier in the disease.

Healthy adults performed significantly better than adults with diabetes on two of the five domains tested: executive functioning, with significant differences across four different tests, and speed, with significant differences or trends across five different tests.

There were no significant differences on tests of episodic and semantic memory, verbal fluency, reaction time and perceptual speed, said an Alberta release.

When researchers divided participants into young-old and old-old, with age 70 as the cutoff, they found the same pattern of cognitive differences between young-old and old-old in the diabetes and control groups.

'Speed and executive functioning are thought to be among the major components of cognitive health,' said co-author Roger Dixon.

According to the US Centres for Disease Control and Prevention, new cases of diabetes nearly doubled in the past decade, with nearly one new case for every 100 adults between the years 2005 and 2007.

Diabetes is a known risk factor for late-life neurodegenerative diseases like Alzheimer's.

These findings were published in the January issue of Neuropsychology, published by the American Psychological Association.